Water softeners of the "ion exchange" type typically include a resin tank through which hard water passes to exchange its "hard" ions of calcium and magnesium for "soft" sodium ions from the resin bed. Regeneration of the resin bed is required periodically to remove the accumulation of hard ions and replenish the supply of soft ions. Regeneration is typically effected by flushing a brine solution through the resin bed. A water softener of this type is more fully described in U.S. Pat. No. 3,891,552 issued June 24, 1975 to William Prior and James W. Kewley, entitled CONTROL VALVE FOR WATER SOFTENERS.
Modern water softeners of the type disclosed in U.S. Pat. No. 3,891,552 typically employ a brine tank which includes a reservoir and supply of salt disposed at a level above the bottom of the reservoir. A tube connected to a source of water establishes a path for water to flow to the reservoir. Upon the attainment of a predetermined level in the reservoir, the water reacts with the salt supply to produce a source of brine for regeneration of the resin bed. When regeneration is required, the brine is aspirated through the same tube that supplied water to the reservoir. The amount of water introduced to the brine tank after the regeneration cycle and the amount of brine aspirated from the tank during a regeneration cycle is controlled by a brine valve mechanism.
Commercially available water softeners generally include one or two tanks which contain the softening chemicals that form the resin beds. In a two tank water softener, one tank is regenerated and kept "off-line" while the other tank is "on-line". A control valve controls the communication of the tanks with the household water supply and controls the timing and sequence of regeneration. An example of such a control valve is disclosed in U.S. Pat. No. 3,891,552. An improved control valve is described in U.S. Pat. No. 4,298,025. Both of these patents are owned by the present assignee and are herein incorporated by reference.
A prior art resin tank typically comprises an elongate cylinder in which the ion exchange resin is contained. A conduit, often called a riser pipe, extends downwardly from the top of the tank. A filter screen, mounted at the end of the conduit prevents the entry of resin into the conduit. An opening is formed in the top of the tank for discharging or admitting fluid depending on the direction of flow.
In many applications, prior art water softeners such as the one described in the above referenced patent, performed satisfactorily. However, in some areas of the country "problem water" is encountered that contains bacteria which, although harmless, does effect the taste and/or odor of the water. The commonly encountered "rotten egg" odor is caused by a non-pathogenic anaerobic bacteria, such as Desulfuviuibrio Desulfuricaus, which is a sulfate reducing bacteria. Normally a food chain is established between the Desulfuviuibrio Desulfuricaus bacteria and an iron reducing bacteria. The reaction carried on by the sulfate reducing bacteria is exemplified by equation A: EQU SO.sub.4.sup.-2 .fwdarw.S.sup.-2 +2O.sub.2 (A)
As can be seen from equation A, the reaction carried out by the sulfate reducing bacteria produces sulfide which when combined with hydrogen produces hydrogen sulfide, a gas having a "rotten egg" odor. The iron reducing bacteria produces carbohydrates which are utilized as food by both the sulfate reducing bacteria and the iron bacteria. The reaction involved is described by equation B: EQU CO.sub.2 +2H.sub.2 S.fwdarw.(CH.sub.2 O).sub.n +H.sub.2 O+2S(B)
Both the sulfate and iron reducing bacteria utilize excess electrons to catalyze their reactions. The required excess electrons are generated by the oxidation reaction of ferrous iron to ferric iron according to equation C: EQU 4Fe(HCO.sub.3).sub.2 +2H.sub.2 O+O.sub.2 .fwdarw.4Fe(OH).sub.3 +8CO.sub.2(C)
Equation C can be simplified to Equation D: EQU Fe.sup.+2 .fwdarw.Fe.sup.+3 +e.sup.- (D)
The simplified equation (equation D) shows the excess electrons produced when iron is oxidized. In short, the odor and the degradation in taste is produced by iron and sulfate reducing bacteria. Both types of bacteria depend on the oxidation of ferrous iron (present in the source water) to ferric iron. In order to carry out the oxidation of ferrous iron, free oxygen must also be available in the water.
It has been found that the use of a water softener may aggravate the problem. In a "two tank" type water softener in which one tank remains off-line in a stand-by condition while the other tank is being used, the idle tank can become a breeding ground for the bacteria. When the stand-by tank is placed on-line, it has been found that at least the initial water discharged by the tank may be of less than optimum quality.